1. Technical Field of the Invention
The invention is generally directed to a method for making enantiomeric organic compounds having high enantiomer excesses using a magnetic field and photolysis radiation.
2. Description of the Prior Art
All objects, including chemical compounds, have a mirror image. However, some objects cannot be superimposed on their mirror image. For example, a left hand and right hand are not superimposable on each other, e.g. a left hand will not fit into a right hand glove. In the case of chemical compounds, these non-superimposable mirror images are called “enantiomers” and are widely used in biological processes.
Chemical compounds are called “chiral” if their mirror images (enantiomers) cannot be superimposed on each other as described above. Some important chiral biological compounds, e.g., amino acids and sugars, are found exclusively as only one of the two possible enantiomers when used in polymers such as proteins and RNA, respectively. These critical biological polymers cannot work (at least, in today's biology) if both enantiomers are present. Since at least the mid-1800s (Louis Pasteur), scientists have wondered how ancient pre-biological chemistry or life forms started such “homochirality” and how to recreate it in the laboratory starting from smaller non-chiral precursors. For example, how would a chemist synthesize only one mirror image of alanine (a simple amino acid) starting from atoms and smaller molecules that should show no preference towards either of the mirror images? Under normal conditions the synthesis will always produce equal amounts of both: imagine flipping a coin several times—the number of heads and tails will be nearly 50-50. There have been a multitude of attempts to create enantiomer enrichments (or “excesses”) in a prebiotic way—both for commercial as well as purely scientific research reasons.
Previous studies of carbonaceous meteorites are relevant to the origin of the present invention as these objects are the oldest (4.6 billion years) in the solar system and therefore their contents are relevant to the study of the first chemical processes. Evidence was found for significant enantiomer excesses in sugar derivatives (sugar acids) in these meteorites: and a natural question was raised about the origin of such a strange phenomenon. (Cooper G., Sant M. and Asiyo C. (2009) Anomalous enantiomer ratios in meteoritic sugar derivatives. Lunar Planet. Sci. Conf. Abs #2537.) Before this work, it was known that some amino acids in meteorites also possessed small enantiomer excesses (Pizzarello S., Cooper G. W. and Flynn G. J. The Nature and Distribution of the Organic Material in Carbonaceous Chondrites and Interplanetary Dust Particles in Meteorites and the Early Solar System II. D. Lauretta, L. A. Leshin, and H. Y. McSween Jr., Eds. University of Arizona Press (2006)). The origin(s) of meteorite enantiomer excesses is still unknown. It is possible that mild photolysis and magnetism may have had a role in the origin of enantiomer excess.
Attempts at using magnetism alone to induce a preference of one enantiomer go back over a century including those by Pasteur to create homochiral molecules in a magnetic field (Mason, S. F., (1984) Origins of Biomolecular Handedness, nature 311: 19-23). To date, there has been no convincing evidence of such a phenomenon (e.g., Bonner, W. A., (1991) The origin and amplification of biomolecular chirality, Origins of Life, 21:59-111; Barron, L. D. (1994) Can a Magnetic Field Induce absolute Asymmetric Synthesis, Science 266, 1491-1492). However, theoretical and experimental studies have suggested or shown that enantiomer selectivity is possible (although extremely small) with the combination of a magnetic field and radiation (light) of parallel, or anti-parallel, direction. Experimental evidence showed that enantiomeric “excess” can be achieved when a pre-made target compound is subjected to a combination of a magnetic field and parallel radiation, see Rikken and Raupach (2000) “Enantioselective mangetochiral photochemistry”, Nature 405, 932-935. These workers placed a K3Cr(III) trix-oxalato complex in very powerful magnetic fields ranging up to approximately 15 Tesla (T) and irradiated it with intense unpolarized light of varying wavelength (approximately 692-701 nm). The complex, which is chiral, then dissociates in an asymmetric fashion, i.e. one enantiomer dissociates slightly more than the other, therefore achieving extremely small “excess” of one of the enantiomers. Maximum excess (˜1.5×10−4) occurred at 695.5 nm and 15T but excesses were observed at lower field strength; from the graph of their data small excesses might be expected at under 3T.
However, there are major differences between past theoretical and laboratory “magnetochiral” work and the present invention. For one example, the past work conducted by Rikken and Raupach used the test compound K3Cr(III) tris-oxolato, which is not biologically relevant and was used in its final form (i.e., it was already synthesized), and its absorption (of light) characteristics were previously well defined. Additionally, the excesses created were extremely small (˜1.5×10−4) and required a laser to measure the difference in abundance of the two enantiomers. The radiation and magnetic field strengths were relatively powerful: the magnetic strength needed for maximum effect (largest enantiomer excesses) was in the range of those used in nuclear magnetic resonance (NMR) while the light source was a laser.
From a scientific point of view, interest in the origins of both homochirality and biologically relevant organic compounds has centered on some of these points: (1) what is the origin(s) of the synthesis of biologically relevant compounds from simpler precursor molecules approximately 3.8 to 4 billion years ago and (2) were there mild (and pre-biotic) methods of producing large enantiomer excesses? It has been known for well over a century that water-formaldehyde solutions easily produce a variety of sugars. The synthesis sequence builds up to at least six-carbon sugars: formaldehyde-a two-carbon compound-three-carbon-four carbon, etc. This reaction, shown in FIG. 1, is known as the “Formose” reaction (Walker J. F. (1964) Formaldehyde. Reinhold Publishing Corp.; Langenbeck W. (1942) Die formaldehydkondensation als organische autokatalyse. Naturwissenschaften 30, 30; Mizuno T. and Weiss A. H. (1974) Synthesis and Utilization of Formose Sugars in Advances in Carbohydrate Chemistry and Biochemistry. Eds. R. Stuart Tipson and Derek Horton, Vol. 29, pp. 173-227, (1974)). Formaldehyde, a one-carbon compound (CH2O) produces these and many other sugars in water solutions. The first compound produced from formaldehyde, the two-carbon compound is called glycoaldehyde and the three-carbon sugar is called glyceraldehyde. The reaction is catalyzed by a base and a divalent metal such as calcium. However, the formose reaction, as with all known non-biological reaction, does not produce compounds containing enantiomer excesses (Mizuno and Weiss, 1974).
Currently, chemical companies do sell some pure enantiomers, however, to attain such enrichments the synthesis ultimately begins from a biological source. In addition to being a time-consuming process, this usually makes the price of enantiomers higher than that of a corresponding non-chiral compound that can sometimes be produced from abiotic (non-biological) synthesis. This can be especially true of the rare (non-biological) enantiomer, which can cost several times more than the common biological enantiomer, if it is made at all.
For over 160 years scientists have attempted to produce abiotic enantiomer excesses in organic compounds. In addition to commercial reasons, scientists want a more plausible explanation of how “homochirality” could have begun in life forms in the Earth's history.